The present invention relates to a device and to a method for shaping a semi-finished fiber product for manufacturing a C-shaped or I-shaped former or rib.
Fibrous composite materials, or fiber composite materials, are being used to an increasingly greater degree in the aerospace industry in order to reduce the weight of structural elements without compromising high load-bearing capacity. Fibrous composite materials are essentially formed from two components: a matrix and the fibers embedded in the matrix. Fibrous composite materials are able to absorb the greatest loads in the direction of extension of the fibers. Hence the direction in which the fibers run or extend is a decisive factor, particularly in the case of curved structural elements. In the case of a C-shaped former or rib for an aircraft, for example, it is desirable for the fibers to always run parallel to one another, both in the area of the web or cross-member, the curvature of which follows the fuselage shape perpendicular to the longitudinal axis of the aircraft, and in the area of the flanges extending perpendicular to the web.
An exact orientation of the fibers would be achievable if one would position each fiber individually on a mold. However, the expenditure of effort for doing so is unreasonably high. Instead the fibers are generally provided as rectangular fiber blanks, wherein the fibers within a fiber blank essentially run parallel to each other. For example, the fibers can run parallel to a longitudinal direction of the fiber blank, at an angle of +45° or −45° (plus or minus forty five degrees) to the longitudinal direction, or perpendicular to the longitudinal direction. If the fiber blanks have already been impregnated with matrix material, then they are also designated as prepreg. The structural element is then formed from a plurality of fiber blanks disposed one on top of the other rather than from a single fiber blank. Such multilayer packages composed of fiber blanks disposed one on top of the other shall henceforth be designated as semi-finished fiber products. However, in this regard it must be pointed out that in principle a semi-finished fiber product can also be made from the single fiber blank. In a semi-finished fiber product, the fibers of the different fiber blanks generally run at different angles with respect to each other. For example, the fibers of sequential or successive layers can always be arranged at an angle of 45° to one another.
In order to form the actual structural element, for example a C-shaped former, the flat semi-finished fiber product must be brought into the future shape of the structural element. In the case of a C-shaped former, this means that the semi-finished fiber product must be shaped such that the web or cross-member follows the curvature or curve of the fuselage shape perpendicular to the longitudinal axis of the aircraft and that the flanges extend parallel to one another and away from the web, perpendicularly thereto. This shaping is generally carried out in two steps: the semi-finished fiber product is first positioned in such a way that it follows the curvature or curve of the web. The web of a C-shaped former, or simply C-former, has two longitudinal edges, of which a first or inner longitudinal edge is shorter than a second or outer longitudinal edge. The different lengths of the first and second longitudinal edges of the former result from the radius that increases over the width of the web and defines the curvature of the web. Because the fibers of the semi-finished fiber product should follow the curvature of the web and should always run parallel to one another, the semi-finished fiber product must be drawn into shape. During this process it is essential to prevent creases from forming along the shorter first longitudinal edge or cracks from forming in the semi-finished fiber product due to substantial tension along the longer second longitudinal edge.
Subsequently, the two flanges are formed by bending or folding the semi-finished fiber product 90°. The problem that the fibers should run parallel when possible arises here as well. For example, fibers running on the web parallel to the longitudinal edges of the web should only run along the web and not across or over the bend between the web and one of the flanges. It is also necessary to prevent cracks or creases, respectively, from forming on the flanges in the semi-finished fiber product. The problem of bulges forming in the transition between the web and the flanges also arises because the radius of the semi-finished fiber product at the transition is larger at the outer layers than at the inner layers, but the layers frequently cannot be displaced relative to one another. These bulges are generally also referred to as book effect. Because an undulation forms in the radius of the semi-finished fiber product and the fibers then raise up in a wave-like manner, the number of fibers per unit volume changes erratically or in an uncontrolled manner. It is essential to prevent this from happening, particularly in the transition between web and flange of a former, because particularly high mechanical forces occur in this zone.
In view of the problems arising from the prior art, the person skilled in the art is faced with the problem of providing a device and a method for shaping a semi-finished fiber product for manufacturing a C-shaped or I-shaped former or rib with which initially some and preferably all of the problems known from the prior art are solved.